Unfortunately, I can't say exactly how I got there, but I had an unsaved file in the editor this morning (Package Body). Since I wasn't sure if I had actually changed anything, I saved the file and looked in git to see if a change showed up there.
Interestingly, only a change in the encoding of German umlauts was detected.
I then closed the editor tab and reloaded the package from schema and saved the corresponding file again (default encoding is UTF-8). After that no more changes were shown in git.
It could be related to the fact that the editor window was loaded from an automatically saved workspace when TOAD was started.